I get that same feeling in my chest. One day I was laying in bed and I had my finger on my pulse when this happened. What I realized is that even though it felt like my heart jumped in my chest, my heart rate didn't change at all. I sat up and belched. Every time I get that feeling, I belch and it goes away (so lady like). ;p Since I have realized it's just gas, it doesn't happen as often or as bad as it used to. I think it's because when I thought it was my heart, I was paying more attention to it, which made it worse. When you get that feeling, try moving your rib cage around and try to burp. I used to get it so bad that it felt like my heart was jumping out of my throat. But, now that I know what it is, it's just not that bad anymore. In fact, my doctor told me that once you realize that the feeling in your chest is normal and not dangerous, it tends to either go away or just not be as bad. She was right.
My big fear is my heart also. Take my advice and try to remember when you get that feeling that it is just gas and try to move around so it will come out.
